1. Field of the Invention
The present invention relates to golf balls. More particularly, the present invention relates to golf balls containing a core and a cover, with dimples being formed on the cover.
2. Description of the Related Art
General golf balls other than those manufactured for use in practice ranges comprise a core and a cover. There exist cores composed of a single solid rubber layer, two or more solid rubber layers, a synthetic resin layer in addition to a solid rubber layer, and the like. The cover requires excellent durability because it is the part the golf ball which contacts with a golf club upon impact and which contacts with the ground surface upon being dropped. To achieve durability, a synthetic resin is often used for the cover.
Conventionally, hardness of a cover has been investigated from various aspects. In general, by making the cover harder, the resilience performance of a golf ball is apt to be improved. To the contrary, by making the cover softer, the feel at impact of the golf ball is apt to be improved. In other words, a golf ball having a hard cover has the defect of an inferior feel at impact, while a golf ball having a soft cover has the defect of an inferior resilience performance.
Thickness of a cover has been also investigated from various aspects. In general, by making the cover thicker, a resilience performance of a golf ball is apt to be improved. To the contrary, by making the cover thinner, feel at impact of the golf ball is apt to be improved. In other words, a golf ball having a thick cover has the defect of an inferior feel at impact, while a golf ball having a thin cover has the defect of an inferior resilience performance. The resilience performance and feel at impact are reciprocal performances.
A golf ball has from about 200 to 550 dimples on its surface. The role of the dimples involves causing turbulent flow detachment by promoting turbulent flow transition of a boundary layer by disrupting the air flow around the golf ball during flight. By promoting turbulent flow transition, the detachment point of air from the golf ball shifts backwards leading to a reduction in the drag coefficient (Cd) so that the flight distance of the golf ball is extended. In addition, the difference in detachment points on the upper and lower sides of the golf ball resulting from back spin is increased by the promotion of turbulent flow transition, whereby the lifting force that acts on the golf ball is elevated.
Specifications of the cover exert an influence upon the behavior of a golf ball and a golf club at impact. To the contrary, specifications of the dimples exert an influence upon the aerodynamic characteristics after impact. Specifications of the cover and specifications of the dimples are considered by the skilled person in this art as discrete factors in terms of performances of a golf ball.
In Japanese Patent Publication Reference JP-A-305114/1998, JP-A-57067/1999, JP-A-225209/2000 and JP-A-70414/2000, there are disclosed golf balls having combination of an optimized cover and optimized dimples.
Even with the techniques disclosed in these publications, specifications of the dimples have been merely comprehended as a factor that exerts an influence upon aerodynamic characteristics. Specifications of the dimples have not been necessarily considered as a factor that exerts an influence upon the behavior of a golf ball after impact. With respect to the behavior of a golf ball at impact, there remains room for improvement. Golfers have always desired to use golf balls that are excellent in terms of both a resilience performance and feel, at impact.